Current methods for completing hydrocarbon wells often involve sequentially pumping fracturing fluids into one or more production zones of a well. In order to improve the efficiency of this process, ball-actuated frac sleeves were invented. The ball-actuated frac sleeve has side ports that block fluid access to a production zone with which it is associated until an appropriately sized frac ball is pumped down from the surface to open the sleeve by landing on a frac ball seat through which the frac ball cannot pass. Consequently, when the stimulation of a zone is completed, a frac ball is dropped or injected into a frac fluid stream being pumped down the well. The frac ball lands on the frac ball seat in the ball-actuated frac sleeve and frac fluid pressure on the frac ball forces the side ports in the frac sleeve to open and provide fluid access to that production zone, while blocking access to the zone that was just completed. If many zones are to be stimulated, a large number of size-graduated frac balls are required to stimulate the entire well without interruption. As understood by those skilled in the art, a diameter of the starting frac ball decreases as the required number of frac balls increases. The use of small diameter frac balls has disadvantages. First, all stimulation fluid must be pumped through the frac ball seat orifices, and each seat is at least marginally smaller in diameter than a diameter of the associated frac ball. If the frac ball seat orifice is very small, the rate at which frac fluid can be pumped into the associated zone is affected. Furthermore, small frac balls are more fragile and more likely to get trapped in casing joints or the like on their way down the well casing.
In order to overcome the first problem, certain ball actuated frac sleeves have two or more small frac ball seats, each having an orifice through which frac fluid can be pumped. This permits higher stimulation fluid throughput, but requires the simultaneous release of multiple frac balls of the same diameter. In order to overcome the second problem, many operators require the injection of two or more frac balls of the same diameter for each frac ball seat when the required frac ball(s) is less than a predetermined diameter. This likewise requires the simultaneous release of multiple frac balls of the same diameter.
Most known ball drops and ball injectors are incapable of, or poorly adapted to, simultaneously drop/inject multiple balls of the same diameter.
There therefore exists a need for a modular ball drop that permits multiple balls of the same diameter to be simultaneously injected into a well.